Pulse generator



Nov. 29, 1955 G. D. BUTLER ET AL 2,725,487

PULSE GENERATOR 6 Sheets-Sheet l Nov. 29, 1955 G. D. BUTLER ETAL2,725,487

PULSE GENERATOR Filed March 4, 1950 6 Sheets-Sheet 2 ATTORNEY Nov. 29,1955 G. D. BUTLER ErAl.

2,725,487 PULSE GENERATOR Filed March 4, 1950 6 Sheets-Sheet I5INVENTORS afa/Paf 0. arm? ATTORNEY Nov. 29, 1955 c5. D. BUTLER Er ALPULSE GENERATOR 6 Sheets-Sheet 4 Jcv-gJoaA/O/WJ/r ATTORN EY Filed March4, 1950 Nov. 29, 1955 G. D. BUTLER ErAL 2,725,487

PULSE GENERATOR Nov. 29, 1955 G. D. BUTLER ETAL PULSE GENERATOR 6Sheets-Sheet 6 Filed March 4, 1950 United States Patent Utilice PULSEGENERATOR George D. Entier, Ridgewood, and Serge A. Loukomsky, NorthPlainfield, N. J., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine Application March 4, 1950, Serial No. 147,7223 Claims. (Cl. Z50-209) This invention relates to an optical-electricalintegrator. More particularly the invention relates to a digitalintegrator for the integration of continuous functions by thediscontinuous summation of selected ordinates.

There are i .any problems where the summation of discontinuousquantities is involved. Essentially, such integrations may be consideredas a process in which areas under successive small arcs of the curve ofthe function to be integrated are represented by the curve ordinate attheir center. Such types of integration permit the use of electronicdigital counters with their inherent enormous speed. Examples of suchproblems are the calculation of integrated tristirnulus values byselected ordinate methods.

When the discontinuous method of integration is used for the integrationof the product of a Xed function by one changing for differentintegrations, a serious problem arises when the fixed function has sharpmaxima. In such cases it is necessary to use a very large number ofareas under very short arcs in these portions of the curve. This entailsvery serious operating problem because if, as is practically always thecase in actual integrations, ordinate values are represented bydisplacements or other physical quantities of a measuring machine, it isnecessary to slow down the cycle of the machine very greatly.

it is, therefore, desirable to reduce the number of selected ordinatesin some portions of the curve of the function to be integrated. in amore specific aspect of the present invention, which, for many problemsis the preferrcd modilication, this is effected by factorial weightingby an intermediate counting circuit, preferably, though not necessarily,of the standard binary flip-dop tube type. By factorial weighting of theordinates in the steeper portions of a curve an excessive number andexcessively close spacing may be avoided.

elected ordinate integration, with or without factorial weighting,necessitates a pulse generating system with switching means and variableintervals during which pulses are generated. in the more specificmodifications it also requires switching means in the weightingcircuits. It is with the pulse generator and its associated switchingand weighting means that the present invention is concerned.

According to the present invention, a disc having two slots at differentdistances from the center is continuously rotated. Two light beams andphotoelectric devices are associated with the slots to effect startingand stopping of the counting of pulses. One of these light sources isrotatable about the axis of the disc and its position determines thenumber of pulsations between the starting and stopping slots. Theangular displacement of the movable light source is controlled by themechanical device measuring the ordinates of the function to beintegrated. Where the preferred modification of factorially weightedordinates is used, other devices, actuated by the ordinate relatingmechanism, control switching in the flip-flop tube circuits.

Various generators for the actual pulses may be used.

Patented Nov. 29, 1955 ln a preferred modification the rotating disc hasa large number of transparent slots on its periphery aligned with a beamof light and photoelectric device, such as a phototube, which generatesan electric pulse every time a transparent slot passes through the beam.This preferred method of generating pulses possesses a number ofadvantages which will be brought out more fully below. However, it isnot necessary that the actual pulses be produced by combined optical andelectrical means. lt is quite possible to produce the pulseselectronically by a suitable crystal-controlled oscillator, which may,for example, opcrate at approximately 1,090 kc., a suitable speed forcounting circuits. lt is then necessary that the disc be rotated at anaccurate speed, which is a sub-multiple of the pulse frequency. This iseasily effected by conventional frequency divider circuits which may,for example, produce a frequency of 5() cycles, which is then used toactuate a synchronous motor which drives the disc at a predeterminedspeed, for example, of the order of 1890 R. P. M.

The pulse generators of the present invention are cheaper to construct,rugged, and present a minimum of maintenance problems. An extremelyimportant advantage lies in the fact that it is not in the leastnecessary that the disc be rotated in synchronism with any operation ofthe measuring machine. ln the case of the preferred generator, in whichthe pulses are formed by combined optical and electrical means, it isnot even necessary that the speed be constant over an extended period oftime. lt is onl,l necessary that speed variations not occur in a time asshort as a counting cycle, which will normally' be of the magnitude of1A() or 1/{50 of a second. Of course, the disc must turn at a reasonablyfast speed so that a normal counting interval will be short compared tothe change of the measuring machine as it generates an outputproportional to the ordinates of the function to be integrated. Thereason why synchronism is immaterial lies in the fact that the number ofpulses which will be counted for any ordinate is determined purely bythe angular displacement of the movable light beam and is independent ofthe ro tational speed of the disc.

The present invention avoids all of the diiculties which have beenencountered in ordinary pulse-generating circuits useful in countingdevices. rthe counting interval magnitude and pulse frequency areautomatically maintained in a fixed relation to each other and, in thereferred modification, pulse frequency can be varied and is immaterialto accuracy. Precision is dependent solely on the number or" pulses fora maximum interval; iu the preferred modification this means number ofperipheral slots. it is easy to obtain minimum precision of the order ofl part in 3,00() with a disc of 3-4 inch radius in the preferredmodification and with disc rotational speeds of the order of 2708 R. P.lvl. in the case of a crystal-contro d. l0() kc. oscillator, the discspeed will be of the order of 18S() P.. P. M. ln the preferredmodification larger discs will give even higher precision, but theminimum, referred to above, is adequate for most ordinary uses.

it is a further advantage of the present invention that theoptical-electrical pulse generator may he used with standard electricalelements and circuits. For instance. a digital counter of the standarddecade type as re tnarly sold on the open marxet may be used, and itsuse re no modicalion. Even when the factorial .veighti the preferredcircuit modification is employed, the flipliop tube circuits are ofstandard design and involve no critical control of any elements.

Electronic circuits of extreme stability and reliability may be used. lnthe preferred modification, pulse frequency is immaterial, and even inother modifications it is only necessary that the ratio of pulsefrequency and rotational speed be maintained constantly. This requiresextremely simple and reliable circuits.

Another advantage of the invention is that none of the replaceableelements, such as phototubes or vacuum tubes, in the electronic circuitsare in any sense critical. It is unnecessary to use matched elements,and there is no change in precision or reliability as an element, suchas a phototube or a vacuum tube, ages; so long as the element operatesat all, the pulse generator and associated circuits of the presentinvention will operate with full precision and reliability.

One of the most important fields for selected ordinate integration is inthe calculation of tristimulus values for colors, using a conventionalrecording type spectrophotometer. Accordingly, in the specilicdescription of a preferred embodiment of the present invention, it willhe described in connection with the actorially weighted, electedordinate integration of tristimulus values. lt ihould be understood thatthe use ot' factorial weighting to the selected ordinate integration oftristimulus values is not our invention. This constitutes the subjectmatter of a copending application of Stearns and Loukornsky, Serial No.147,721, tiled March 4, 1950, now Patent 2,603,123 issued July 15, 1952.The pulse generating system of the present invention is eminently suitedfor use in the system of the Stearns and Loukomsky application, and isdescribed therein as a preferred type of pulse generator. lt should beunderstood, however, that the two inventions are unrelated, since theresults of the Stearns and Loukomsky device may be obtained with anysuitable pulse generator; and the pulse generating and counting systemof the present invention may be used in any device for selected ordinateintegration regardless of whether or not it involves spectrophotometricmechanisins.

The invention will be described in greater detail in connection with thedrawings in which:

Fig. l is a semi-diagrammatic plan view of a flickering beamspectrophotometer, pulse generator and weighting l system;

Fig. 2 is an enlarged vertical elevation of the pulsegenerator, partlyin section, along the line 2-2 of Fig. l;

Fig. 3 is an enlarged end view, partly broken away, o thepulse-generator;

Fig. 4 is an enlarged detail elevation of the ordinate selecting andweighting means;

Fig. 5 is a plan view of the ordinate selecting cam;

Fig. 6 is an enlarged detail of a portion of the ordinate selecting camand corresponding microswitch;

Fig. 7 is a developed surface of the edges of live of the weightingcams;

Fig. S is a diagrammatic representation of the electronic circuits ofthe pulse-generator, weighting and counting devices;

Fig. 9 is a schematic diagram of the gating circuit; and

Fig. l0 is a diagrammatic representation of a modified pulse generatorin whichV the pulses are generated electronically.

Fig. l illustrates the application of the pulse-generator and integratorto a standard type of recording iiickeringbeam spectrophotometer asdescribed in the Pineo Patent 2,107,836. Since the spectrophotometer isof conventional design, only the portions directly cooperating with thepulse-generator, weighting and integrating means are shown in detail.

The conventional Van Cittert double monochromator of thespectrophotometer is shown at l. The monochromator is operated in theusual manner by the wavelength-changing rod 2 engaging with one of thewavelength carns 3 on the shaft lil driven by the motor 9 throughgearing, which will be described below in connection with Fig. 4, andthe worrn ll. rlhe same drive actuates the conventional recording drum12 of the spectrophotometer.

The spectrophotometer operates in its customary manner, themonochromatic light from the monochromator passing through aphotometering Rochon or Nichol prism 4, rotatable by the cam follower 5,which contacts a linear record cam T14. This cam provides shaft rotationproportional to the square of the tangent of the angle through which thephotometering prism 4 is turned. The polarized beam is then split intotwo by the conventional Wollaston prisms, the two beams flickered inopposite phase in the usual manner, and passed through transmissionsample holders 6 into an integrating sphere provided with reflectancesample holders 7 and 8. Unbalance of light in the integrating sphere aticker frequency, due to differential transmission or reflectance ofsample and standard, is then ampliiied in the usual manner by ahigh-gain iiicker frequency amplilier (not shown), and actuates thephotometering motor 13 to turn it in a direction to rotate cam i4,through highreduction friction transmission, to rotate the photometeringprism 4 so as to restore the total light in the integrating sphere tobalance.

A steel tape on a pulley on the shaft of the cam 14 drives acorresponding pulley 16 in the pulse generator, the steel tape beingkept taut at all times by the cable 35 and tightening spring 36. As aresult the pulley 16 is rotated in proportion to changes in thepercentage transmission or reflectance of the sample whose integratedvtristimulus values are to be evaluated.

The pulse-generator of the present invention is a cornbined optical andelectrical device, the optical-portion elng illustrated in enlargeddetail in Figs. 2 and 3.

The pulley lo is keyed onto a shaft 17 journalled in three supportingcolumns i8 on a framework 19. On this shaft there are keyed two parallelarms 20 and 21. The rst carries a light source 22 and collimating lens23; and the second a slot and a bent rod 24 of transparentmethylmethacrylate resin. The rod enters the light-tight housing of theelectrical portion of the device through a hole concentric with theshaft 17 and serves to lead light into said housing.

A second light source 3l, with collimating lens 32, directs a parallelbeam throughv two openings iri one leg of a mask 37. In thecorresponding opening in the other leg are two slots mounted ontransparent methylmethacrylate plastic rods 33 and 34 also entering thehousing of the electrical portion of the device. The three rods 24, 33and 34 lead the light beams striking their faces to three phototubes 40,3S and 42 respectively, from whichroutput wires 41, 39 and 43 lead intothe electronic portion of the device, which will be described below.

Between the right-hand supports i8 there is mounted on the shaft 17, inball bearings, a hub 26 carrying a glass disc 25 which is rotated at ahigh, but not necessarily synchronous, speed of approximately 2700 R. P.M. The drive is through the pulley 27 and belt 23. A housing 30surrounds the upper edge of the rotating disc.

The disc, which is cut from a photographic negative plate, is providedwith a series of narrow, clear portions, or slots, 46 (Fig. 3), aroundits periphery. These slots, which are uniformly spaced, number 3600.Just inside the row of slots there is a single slot 45 which will bereferred to as the stopping slot, and still nearer the center, astarting slot 44 displaced from the stopping slot byl a predeterminedangle, in the device illustrated, 30. The rest of the disc is opaque,and its rotation is counter-clockwise as shown by the arrow along itsperiphery.

Thearm 21 is shown in three positions, A, B and C, the lirstcorresponding to a position for which the operation'of the device willbe described below, while B and C show the arm in the two extremepositions corresponding to zero transmission or reflectance of thespectrophotometer, or respectively. In positions B and C the arm 2l isexactly 30 from the openings in the mask 37.

Flashes of light through the starting slot 44 start the electroniccounting circuits as will be described below,

and, as its name indicates, a stopping slot 45 stops counting. In theposition A it will be seen that the starting slot 44 is almost oppositethe end of the rod 24. As it passes, a pulse of light through the rod 24is transformed into an electrical pulse by the phototube 40 and startsthe counting circuits as will be described later. Then each flashthrough the rod 34, as the slots 46 pass in front of it, is transformedinto an electrical pulse by the phototube 42 and is counted. When thestopping slot 45 passes in front of the rod 33, the resulting flash istransformed into an electrical pulse by the phototube 38 and stops thecounting circuits.

It will be noted that the number of flashes from the slots 46 which arecounted, is proportional to the angular position of the rod 24, that isto say, to the percentage transmission or refiectance measured by thespectrophotometer at a particular wavelength.

In the position B the starting fiash and the fiash occur one rightbefore the other. or transmission is therefore represented by a singlecounted flash. In position C, corresponding to 100% reectance ortransmission, there will be 3,001 ashes counted.

In order to operate the machine, it is necessary that the ordinates beselected and that the proper weighting be given to each ordinate. Thisis effected by a splined, detachable sleeve 47 which slides down on theshaft 1G (see Fig. 4), the shaft being journalled in the mounting 57.The drive is by motor 9 through worm 59, worm wheel 49, worm 11 and wormwheel 53. The reduction is such that the shaft 1t) makes somewhat lessthan a complete revolution in two minutes, which is the standardoperating cycle of the spectrophotometer. The wavelength cams 3determine the range of the spectrum through which the monochromatormoves, and, for clarity, in Fig. 4 the rod 2, moved by the cams 3, isomitted.

The sleeve 47 carries seven cam discs Si) to Se, spacing beingmaintained by the spacers 4S, which serve to make the whole assemblyrigid. Engaging with the edges of each of the cam discs, arecorresponding microswitches 60 to 66. From each switch emerges a pair ofwires which will be designated for clarity by the number of the switchwith the subscript w. in other words, the wires from switch 60 will bedesignated 63W.

Disc 50 is the ordinate-selecting disc, and is provided with a series ofnotches 68 distributed non-uniformly around its periphery at the angularpositions corresponding to the position of the shaft at differentwavelengths of the selected ordinates.

The microswitch 60 engaging the periphery of the disc 50 is providedwith an actuating arm 67 (Fig. 6). rThis is a conventional design ofmicroswitch and hence the actuating arms of the other microswitches 51to 66, which are shown on Fig. 4, carry no reference numerals. They areof similar shape to 67.

When the arm 67 of the switch 6d drops into an ordinate-selecting notch68, a circuit is closed through the Wires 60W, which activates theelectronic circuits of the counter and weighter so that they can respondto pulses from the starting, counting and stopping slots, only one foreach closing of switch 60. This is necessary as the disc 25 makes morethan one revolution between notches, and may make more than onerevolution while switch 6i) is closed.

Discs 51 to 56 correspond approximately to tristimulus for daylight(illuminant C). Since a maximum weighting ratio of 1:16 suffices forthis tristimulus, disc S1, which corresponds to a weighting of 1, doesnot have any indentations and therefore its rnicroswitch is not actuatedwhen the integral value of this tristimulus is being measured. Thesmallest weighting, a weighting of 2, is provided by disc 52 and as disc56 provides for a weighting of 32, the ratio of 16:1 is maintained.

Fig. 7 shows the peripheral surfaces of discs 52 to 56 rolled out in astraight line. Disc 51 is not shown as it has a smooth surface. It willbe noted that the indentaflash of light through the stopping Zeroreilectance tions 69 give various weights for different groups ofselected ordinates, disc 51 corresponding to a weighting of l, 52 to 2,53 to 4, etc. It will also be noted that the areas in the spectrum wherethe same weighting is employed, correspond roughly to the curve of thetristimulus function, the surface reading increasing in frequency fromleft to right because of the direction of rotation of the discs, whichis the opposite of the conventional representation of spectral curves.

The operation of the electrical pulse-generator weighting and countingcircuits will be described in connection with Fig. 8, which is a blockdiagram, as the electronic circuits consist 0f known elements. Pulsesfrom the starting phototube 40 are carried through wires 41 to a pulseamplifier and shaper 77 of conventional design. In a similar manner, thestop pulses from phototube 38 are carried through wires 39 to the pulseShaper and an amplifier 78, and the pulses from the counting phototube42 through wires 43 to the amplifier 79. A gating circuit 70 has acircuit activating the gate, which circuit is actuated through wires 60Wand amplifier 80. The output of the amplifier 77 is then able to openthe gating circuit so that the pulses from amplifier 79 pass through.The circuit is inactivated by a pulse from amplifier 7S, which re-setsit so that it is necessary for it to receive first a pulse through wires60W, and then from the amplifier 77, before it again opens. The countingpulses pass to the gating circuits 71 to 76, which are actuated by theclosing of microswitches 61 to 67 respectively. These gating circuitslead into the inputs of binary flip-dop tube circuits S1 to 85 servingas weighting counters and direct to the input of the six-decade digitalcounter S6 respectively. When microswitch 61 is closed, the pulsespassing through the gating circuit 70 are impressed on the input circuitof the first iiip-iiop tube circuit 81. They are counted through thefive flip-flop circuits, and then into the digital counter. In otherwords, there is a pulse in the input of the digital counter for everythirty-two pulses in the input circuit of the first flip-flop tubecircuit 81. If a different weight is called for for a particularordinate, for example a weight of eight, a depression in the disc S4engages with the ac tuating arm 64, and the counting pulses are thenapplied directly to the input circuit of flip-flop tube 84. In this casethere will be a pulse in the input of the digital counter for every fourpulses. Where a weighting ratio of 32:l is required, as in the case ofthe Z tri-stimulus for illuminant A, there will be a depression on thedisc 51, which Will aetuate the microswitch 66 and the gating circuit 71so that the counting pulses will be applied to the first weightingcounter 84.

The operation of the gating circuit 70 will be described in connectionwith Fig. 9 which is a schematic diagram of the essential elementsthereof. The gating circuit consists of two pairs of fiip-flop tubes 87and 88, and 89 and 90. The flip-dop tubes are connected to a source ofB-fvoltage in the usual manner through plate resistors 9i-94, the lastone being tapped and connected to the cathode of a diode 95. The plateends of the resistors 91-94 are connected in the usual manner to thegrids of the opposite tube of each pair through the conventional RCcircuits. The grids are provided with grid resistors, and the cathodesof each pair are connected to ground through the usual by-passed biasresistors. One of the wires 69W from the output of a trigger actuated bythe ordinate selector is connected to the plate end of the resistor 91,and the outputs of the start and stop amplifiers 77 and 78 are connectedrespectively to the plate ends of the resistors 93 and 94. The latterpoint is also connected through two resistors in series to a source of20-30 volts negative bias. The junction point of the two resistors isconnected to the grid of tube 96, which furnishes voltage for a gatingcirciut connecting the pulse amplifier 79 to the weighting-gatingcircuits 71 to 76. The plate end of resistor 92 is connected to theplate of the diode 95 and through two resistors in series to thenegative 30vo1t bias- 7 ing voltage source. The junction of the tworesistors is connected to the grid of a cathode follower tube 97, thecathode of which is connected to the cathode of a diode 98, the plate ofwhich is connected to the grid of the last stage of amplifier 77.

All pulses actuating the gating circuits are negative pulses. ln itsnormal condition, triodes S8 and 9i) are conducting, and triodes 87 and8% are biased to cut-off. ln this condition the voltage at the plate endof resistor 92 is low and, accordingly, triode 97 is not conducting, andtherefore its cathode, and hence the cathode of diode 9S, is at groundpotential. This diode effectively short-circuits the signal to the laststage of amplifier 77, and no start pulses are present in the output ofthis amplifier. Also, cathode follower 96 is at cut-olf and no positivegating voltage is available.

When the microswitch 6l) drops into a notch on the disc t), a negativepulse is applied by the amplifier Si) to the plate end of resistor 9iand through the RC circuit to the grid of tube 3S. The latter is dippedto the non-conducting position, and the resulting high Voltage from theplate end of resistor 92 starts the tube 37 conducting, the resultantlow voltage at the plate end of the resistor 9i maintaining lthe grid oftube 8S biased to cut-off. The high voltage from the plate end ofresistor i2 overcomes the bias on the tube 97, which starts to conduct,raising the voltage of the cathode of the tube so that the latter ceasesconducting, and the output stage of amplifier 77 is therefore no longershort-circuited. rfhe diode 95 begins to conduct since its anode is athigher potential than the cathode but the positive pulse applied to thetap of resistor 94 is insulhcient to start tube 3% conducting. The tubes89 and 90 are now set for response to starting and stopping pulses. Whenthe starting slot in the disc registers with the starting beam, anegative pulse is delivered to the plate end of the resistor 93 andthence to the grid of the tube 90. The latter iiips to thenon-conducting position, tube S9 conducting. rl`he plate end of resistor94 is now at high potential which overcomes the cut-off bias on tube 96,a corresponding positive voltage being impressed from its cathode to thegate circuit for the pulse amplifier 79, unlocking the latter in theconventional manner and permitting pulses from the amplifier 79 to reachthe gating circuits '7 1 76, one of them being energized by the weightselector cams 5ft-56 so that the gate for the proper weighting isopened. iulses from amplifier 79 are counted by the digital counterthrough the weighting circuit chosen. Diode 9S stops conducting whentube 9G becomes noncondncting, resulting in a positive pulse at theplate end of resistor 92, which also acts on the grid of the conductingtube 37 and hence does not flop the pair 37, 33.

When the stop slot in the disc registers with the stopping beam, anegative pulse is applied from the amplier 73 to the plate end ofresistor 94 and thence to the grid of tube 89. The tubes then iiop backto their original state with the tube 90 conducting and tube S9 biasedto cut-off. The lower'voltage in resistor 9d permits the diode 95 toconduct, thus applying a negative pulse to the grid of the tube 87,causing this pair of tubes to flop to the original position; at the sametime, tube 37 is biased to cut-off, diode 98 begins to conduct, and thestarting amplifier 77 is shortcircuited. The low voltage at the plateend of resistor 9d also results in biasing the tube 96 to cut-olf, whichcloses the gate to the weighting and counting circuit. Succeeding stoppulses have no effect on the syster because the tubes 89 and 90 arealready in the flopped position, which results from a stop pulse.

It will be apparent that every ordinate on the disc Sil corresponds to aparticular position in the spectrum, The transmission or reflectancemeasured by the spectrophotometer will determine the angular position ofthe rod 24 and hence the number of iight pulses impressed on thephototube 42 between start stop. At the same time, one of the weightingdiscs, through its microswitch," will connect the pulses to the properportion of the weighting circuit so that the number of pulses will begiven the proper weight. For the usual two-minute cycle of thespectrophotometer, the number of pulses counted are well within the kc.response of the digital counter and weighting circuits, and at the endof the cycle the decade counter will give a number corresponding to theintegrated tristimulus value of the particular tristimulus for aparticular illuminant. AnotherV set of discs for the next tristimulusare then slipped onto the shaft lt?, and the operation repeated untilthe integrated values for three tristimuli are obtained. lf it isdesired to obtain the integrated tristimulus Values for anotherilluminant, the cycle is repeated three times with sets of discs for thetristimuli for the second illuminant.

Fig. l0 illustrates a modified pulse-generator in which the pulses aregenerated electronically. Elements common to the other figures are giventhe same reference numerals. 'The disc 25 is provided only with startingstopping slots 44 and 45, and only the light beams and photoelectricelements operating with the starting stopping slots are included. Pulsesare generated by the crystal-controlled oscillator 99, of conventionaldesign, which mai for example, operate at l0()` These pulses are fed tothe pulse amplifier 79. The sine wave of the oscillator is shaped by theamplifier. A pulse of 10i) kc. signal is fed through a frequency divider10i), producing a sub-multiple frequency of 50 cycles, which operatesthe two-phase synchronous motor lult to drive the disc at about 1800 R.P. M. in constunt proportion to the oscillator frequency. The frequencydivider includes conventional amplifier and phase-splitting circuits toproduce a two-phase output of sufficient power to operate motor lill.

The operation of the device is exactly the same as the preferredmodilication shown in the preceding figures. Here, as there, the numberof pulses is determined solely by the angular displacement of one of thelight sources and its associated photoelectric device, in the ligure thestarting light source 22 and the bent rod 24 carrying a slot at its end.The number of pulses for a maximum displacement is still 3,001, and theaccuracy of the device is in no way dependent upon an absolutelyunchanging oscillator frequency. Even if this frequency changesslightly, for example by temperature changes which affect the crystalfrequency, there is no change in precision for the frequency divideralways causes the disc to rotate at a speed proportioned to theoscillator frequency. As the latter increases, the speed of rotationincreases in proportion and vice Versa.

ln the preferred modification, the pulse frequency is always the sameconstant multiple of the disc R. P. M., and the ratio can not be changedbecause it is inherent in the structure of the disc. In the case of themodified pulse-generator illustrated in Fig. l0, however, the relationbetween frequency and disc R. P. M. can be varied. For example,conventional switching in the frequency divider can change the frequencysupplied to the motor lill. For any given setting of the switch,however, the ratio is constant. The frequency will be referred to in theclaims as a predetermined constant multiple of disc rotation."

Frequency dividers often divide the frequency factorially and in such acase the frequency divider may be used in place of weighting counters inorder to give diierent weights to different ordinates for uses such asare described in the present specification where fractorial weighting isemployed. Even though the ratio of frequency to disc rotation may bechanged during a particular measurement, it is always constant for anyone cycle, and all of the advantages of precision and ac curacy areretained regardless of whether the predetermined constant ratio existsfor the whole of a measurement or for one or more ordinates.

In the specific modifications described, the starting light beam and ligt conducting rod are shown as movable. Exactly the same results areobtained if the stopping beam is made movable and the starting beamfixed, the respective slots, of course, being located in the correctangular relations. lt would, of course, also be possible to have bothbeams movable but for most opcrations in which a single physicalquantity proportional to the ordinate, such as displacement, isgenerated by the measuring machine, it is only necessary to have one ofthe two movable. Where, however, two quantities are produced by ameasuring device and it is desiredl to integrate by the selectedordinate method a differential between the two quantities, such, forKample, as their arithmetic difference, one quantity can move thestarting light beam and the other the stopping light beam., In otherwords, the angular portion of one or both starting and stopping beamsmay be controlled by the output of one or more measuring devices. Thesum of the puise generated is always directly proportional to the anglebetween the two light beams minus the angle between the start and stopslots on the rotating wheel.

The spinning disc may be of any suitable material and the slots may betransparent portions or they may be cut out. The preferred constructionis by photographic means, the peripheral slots being drawn in India inkon a large circle, for example four feet in diameter. This is thenphotographed onto a glass plate so that the circle is of the desiredradius. The black slots appear on the negative as clear glass, and theplate is then cut to form a circular disc and fastened at its centeronto a suitable iub. The photographic method of construction is not onlycheap and reliable for a single device, but permits the production of anunlimited number of discs from a single drawing.

The pulse-generator of the present invention has been shown inconnection with digital counting circuits. This is its most importantfield. However, in its broader aspects, it is not limited to a countingor integrating device, for the series of variable timed bursts of pulsescan be used for any purpose where such a signal is de sirable.Accordingly, the invention is not limited in its broader aspects tocombination of the pulse generator with electronic mounting circuits. Ina preferred modilication, however, such a combination is included as itconstitutes the most important field of utility for the presentinvention.

In the specification reference is frequently made to gating circuits. Itwill be noted that these gating circuits do not necessarily all operateby the same electronic principle, and this is well illustrated by Fig.9. Most of the gating is effected by the very common method of biasing atube in a circuit to cut-off. There are, however, other well-knownmethods of negativing a circuit, one of which is illustrated by thediode 98 which absorbs the signal in a stage of the amplifier to whichit belongs thus eectively short-circuiting the stage for certain typesof signals. It should therefore be understood that in referring togating circuits in the speciiication and claims it is not intended tolimit them to those in which circuits are activated and inactivated bygrid bias changes.

We claim:

l. A pulse-generator comprising a rotatable disc having two single slotsat different distances from the center; means for rotating the disc,means for generating electrical pulses at a frequency which is apreselected constant multiple of disc rotation; means for generating twolight beams at right angles to the rotatable disc, one of said beamsbeing spaced from the center of rotation of the disc a distance equal tothat of one of the single slots so that it registers with one of thesingle slots at one angular position in the rotation of the disc and theother beam generating means being spaced from the center of rotation ofthe disc so that the beam produced registers with the other slot when itpasses the beam; means for directing the light from each of the beamsafter passing through the respective slots onto photoelectric devices;means for movina in a circle concentric with the axis of rotation of therotatable disc the beam generating and beam directing means of at leastone of the beams, said means moving the beam generating and beamdirecting means in unison; a gating circuit connected to the pulsegenerating means and actuated by the output of the photoelectric devicescapable of starting and stopping transmission of the electrical pulses.

2. A pulse-generator according to claim 1 in which the means forgenerating electrical pulses is a large number of transparent slotsaround the periphery of the disc, and means for generating a light beamstriking the peripheral slots, and means for directing said beam afterpassing through said slots, onto a photoelectric device.

3. A device according to claim 1 in which the means for generatingelectrical pulses is an electronic oscillator and pulse-shapingamplifier, means for rotating the disc is a synchronous motor and aportion of the oscillator signal is connected through a frequencydivider to actuate the motor.

References Cited in the iile of this patent UNITED STATES PATENTS

